Battery Cut Off Switch Ideas

[304065]

As far as blowing the alternator or other things, why is disconnecting the battery different than switching off the ignition? How about in a double plug engine with twin CD boxes and switches to control them?

Mike,

The modern FIA switch (like the Sparco used in the Cup Cars) has six poles:

2 Big ones- normally closed-- open the switch to disconnect battery
2 little ones- normally closed- open the switch to disconnect power to ignition system
2 little ones- normally OPEN- close the switch- this makes a circuit between the lead from the alternator to a 10W, 3 ohm ceramic resistor, with one end on the pole of the switch and the other end on ground.

When you throw the switch in addition to cutting off the battery and ignition you connect the alternator's output to the resistor. As written above, normally when the battery abruptly comes out of the circuit the alternator voltage skyrockets which can cook the output diodes and fry sensitive electronics in the car. So by connecting the resistor, the alternator's output heats up the resistor for a few microseconds until the residual magnetism in the rotor dies down and the alternator output goes flat.

Does that matter? Yes, even though it's only a short time, it's a long time from a physics perspective.

[JohnT]

Showing my age again Ed? Good thing I appended the "er, I think."

I vividly remember sitting in a tech line with a 2 pole shut off when the inspector said "start the car" and then switched off and removed the key with absolutely no effect! Now I have a 4 pole.

thanks for the education Ed.

[keith]

sorry to resurrect an old thread, but I'm wondering:

A) what did you end up doing John?
and B) what about switching the big positive cable from battery to starter for anti-theft? seems like it would be easy enough to route it up to the speaker location/switch (if going historic on placement) and then a lead from switch to battery - and would only disable starter, no?

(what am I missing?)

[ejboyd5]

Always thought the smuggler's box was a good place to put the disconnect switch. Following prevailing practice, it is the negative lead that is switched using the Hella unit with the removable red handle.

[trdking]

Mike,

The modern FIA switch (like the Sparco used in the Cup Cars) has six poles:

2 Big ones- normally closed-- open the switch to disconnect battery
2 little ones- normally closed- open the switch to disconnect power to ignition system
2 little ones- normally OPEN- close the switch- this makes a circuit between the lead from the alternator to a 10W, 3 ohm ceramic resistor, with one end on the pole of the switch and the other end on ground.

When you throw the switch in addition to cutting off the battery and ignition you connect the alternator's output to the resistor. As written above, normally when the battery abruptly comes out of the circuit the alternator voltage skyrockets which can cook the output diodes and fry sensitive electronics in the car. So by connecting the resistor, the alternator's output heats up the resistor for a few microseconds until the residual magnetism in the rotor dies down and the alternator output goes flat.

Does that matter? Yes, even though it's only a short time, it's a long time from a physics perspective.

304065, These are excellent suggestions for protecting the car all around. I am not sure that everyone wants to add all that hardware to an original car? Years ago I was a partner in an Alarm security company that was creating effective vehicle security systems for cars and motorcycles. and not to bust your bag but for the purpose of this I need to state that no switches are "Normally" anything. They are manually moved to positions. The most basic being on and off or open and closed. Solenoids turn a manual switch into an electronic switch by adding a secondary power source to a solenoid outside of the switched system to control its function by adding or taking power away. This created the two pole positions in relation to how the switch reacts when power is applied. Thus a switch that is closed at rest is Normally closed and a switch that is Open at rest is Normally open.
I do see that when the two functions of the switch are closed it opens the resistor circuit. Brilliant idea.

Probably too much explanation but I twisted my ankle pretty good this weekend and I am on some pretty decent pain killers.

Anyway, we developed a simple but effective kill switch using 1 normally closed and one normally open solenoid switch each integrated respectively into the horn circuit and the ignition switch circuit So that when the ignition switch was held in the crank engine position the only thing that would happen is it would open the horn circuit and disable the horn
No Start. You would then have to complete the circuit power to the normally open ignition circuit by completing the ground by pressing on the horn button. Car start. When the ignition switch went back to the rest position after start it would then close the horn circuit and the horn would function properly while driving. It was effective and did not require the addition of a manual switch inside the cab. Just a thought. We tested it out with former car thieves at the time and not one of them thought to push the horn button during start. and could not figure out why they could not get voltage to the starter solenoid.
THis of course is only a kill switch not a cut off switch as this post is titled but thoought I would share the idea for those looking for an effective kill switch.
Cheers all.

[keith]

we developed a simple but effective kill switch using 1 normally closed and one normally open solenoid switch each integrated respectively into the horn circuit and the ignition switch circuit So that when the ignition switch was held in the crank engine position the only thing that would happen is it would open the horn circuit and disable the horn
No Start. You would then have to complete the circuit power to the normally open ignition circuit by completing the ground by pressing on the horn button. Car start. When the ignition switch went back to the rest position after start it would then close the horn circuit and the horn would function properly while driving. It was effective and did not require the addition of a manual switch inside the cab. Just a thought. We tested it out with former car thieves at the time and not one of them thought to push the horn button during start. and could not figure out why they could not get voltage to the starter solenoid.
THis of course is only a kill switch not a cut off switch as this post is titled but thoought I would share the idea for those looking for an effective kill switch.
Cheers all.

Great approach!

[dirk07]

Any modern six pole cut off switches with the old Bosch SSH 15/12Z optic on the market?

[uai]

Perhaps one of these takes an old bosch key - calling them could be an idea
http://www.kissling.de/de/produkte/b...etrennschalter
The CEO of the company has a weak spot for historic cars - he has a nice collection of even nicer prewar Cars.
Otherwise you could jbweld something to your Bosch key

[keith]

revisiting this; and looking at this RSR diagram, it seems that the factory didn't interrupt the battery-starter-alternator leg at all, correct..? (my squinty german is rusty)

[chris_seven]

The common 'Autolec' switch is a relatively poor device and they don't have a good record for reliability particularly when left in an 'off' postion for long periods of time. On a Rally Car I would replace them every year.

We gave up using them many years ago. There are several replacment devices on the market and they commonly use sophisticated solid-state relays The most commonly used devices seem to be made by Caretk.

They work well and use a 'latching' type relay which is permanently powered and as well as the 'kill' switch there is an additioal on/off switch to remove all power to the relay and prevent the battery from flattening when the car is parked for a long period.

When you 'forget' to tuen them off they are a PITA and they are expensive.

We have used a more straightforward method for the last 15 years by using a High Current Relay which is non-latching We use a Tyco EV200 Relay .



This relay is also solid state and is unaffected by vibration and shock which can be an issue with mechanical relays.

It is intrinsically safe and won't spark and has two auxillary contacts so you can also switch off the ignition warning light circuit which can still allow the engune to run when the battery is isolated.

The switch that operates this syetm needs to be a relatively high current 'latching' switch and we use a switch with a 20A current rating.

We protect alternators using a TVS Zener Diode.

http://www.littelfuse.com/~/media/el...n_note.pdf.pdf

If you just want to stop the car from being started just put a switch in the ignition circuit.